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Copper is still the monometallic electrocatalyst of choice for electrochemical reduction of CO2 (ERC) when added‐value products, such as hydrocarbons and alcohols, are desired. However, severe morphological and structural changes are observed upon exposure to the ERC operation conditions. One of the pending questions in the community is what the mechanism behind this reconstruction is. In the present study, pulse‐electrodeposited copper nanoparticles were exposed to different ERC relevant reductive potentials and tracked with identical location scanning electron microscopy (IL‐SEM). This approach provides information on the morphological and structural history and subsequent change of Cu nanoparticles and with that a deep insight into the reconstruction events. With this evidence, we could interpret the observed structural changes as two separate electrochemical processes occurring one after another, namely copper dissolution from pre‐oxidized native nanoparticles and subsequent (electro‐) redeposition of the dissolved copper species in a form of new smaller Cu fragments. [ABSTRACT FROM AUTHOR]

The rational design of electrochemical oxygen evolution reaction (OER) electrocatalyst is essential for the development of efficient and sustainable electrochemical energy conversion, storage and electrolysis applications. One of the remaining limitations of the low‐temperature electrolyzers is the large amounts of highly scarce and expensive iridium used as the OER electrocatalysts. This could be solved by applying much smaller amounts of iridium on efficient and stable support. Here we present a very promising functionality of titanium oxynitride (TiONx) high‐surface‐area support that effectively disperses the iridium nanoparticles, exhibits good intrinsic electrical conductivity and stability and thus promises efficient reduction of the noble‐metal loading in electrolyzers gas diffusion electrodes. The new nanocomposite made of approximately 3 nm‐sized iridium nanoparticles finely dispersed on TiONx support is produced using a novel synthetic route. Extensive characterization shows that the new composites exhibit an electronic interaction with the support and, ultimately, a high OER performance in acidic media. [ABSTRACT FROM AUTHOR]

Pt-based nanoparticles supported on high-surface-area carbon (HSAC) show very good properties as catalysts in polymer electrolyte membrane fuel cells (PEMFC). In many cases, however, the initial high activity of such catalysts rapidly drops as caused by various detrimental phenomena occurring in a typical electrochemical environment. In this work, a detailed study of a highly active system composed of PtCu3/HSAC nanoparticles with partially ordered structure and Pt skin with the addition of Au is performed. By using aberration-corrected scanning transmission electron microscopy, the effects of adding small amounts of gold compared to the nonmodified sample are followed through the different stages of an electrochemical cycling degradation protocol. Various morphological changes such as faceting, reshaping, and thickening of the Pt skin are investigated for both sets of samples on the atomic level. Interesting features such as well-defined shapes and surface defects are observed after degradation. However, the most important differences in terms of durability seem related to particle porosity. Finally, the experimental morphological observations are successfully reproduced by dealloying simulation with kinetic Monte Carlo modeling. [ABSTRACT FROM AUTHOR]

Crystalline Cu3Pt nanoparticles supported on graphitized carbon are synthesized by using a modified sol-gel method, and subsequent thermal annealing leads to alloying of Pt with Cu and formation of a partially ordered Pm ${\bar 3}$ m structure. Electrochemical dealloying under potentiodynamic conditions (potential cycling) induces not only changes from rather spherical high-index faceted to more cuboctahedral low-index faceted core-shell structures for particles in a size range of 10-20 nm but also percolation for some particles larger than 20 nm. In contrast, during dealloying under potentiostatic conditions (potential hold) the semispherical shape of small particles is completely retained and extensive porosity is formed on all particles larger than 20 nm. Other degradation processes are not observed on performing an additional accelerated aging test; hence, the high specific and mass activity of the catalyst decreases only slightly, mainly owing to continuing Cu leaching. The difference in dealloying protocols and their effect on the structure of the catalysts as well as their activities, considering the promising porosity formation, are discussed and indicate future directions for a rational design of active and stable oxygen reduction reaction catalysts. [ABSTRACT FROM AUTHOR]

Abstract: A series of Pt-skin type catalysts has been synthesized in order to substantially enhance their specific and mass activity in MOR and ORR — two reactions known to have high activation polarization. Due to strain and ligand effects the Pt-skin catalysts shift the ORR potential to higher values by 50mV. Adding Ru to the most active PtCu/C ORR catalyst creates a wider potential window in which MOR has a five-fold current density with respect to commercial PtRu (1:1)/C catalyst. [Copyright &y& Elsevier]

B The Front Cover b shows titanium oxynitride nanoribbons with finely dispersed iridium nanoparticles as an oxygen evolution reaction electrocatalyst. In their Full Paper, Nejc Hodnik, Miran Gaberscek and co-workers describe how Ir nanoparticles dispersed on the titanium oxynitride nanoribbon show promise to be used as proton exchange membrane electrolysis anode electrocatalyst. Electrocatalysis, PEM electrolyzers, oxygen evolution reaction, titanium oxynitride, stability. [Extracted from the article]

Water splitting in acidic media is a sustainable and efficient new way to produce hydrogen fuel. However, the main bottleneck preventing the wider use of electrolyzers is still the oxygen evolution reaction (OER). Currently, the best electrocatalysts for OER are Ir-based materials, but the mechanistic details are still not fully understood. In this work, we investigate the similarities and differences in the OER mechanism of three different Ir-based catalysts, namely Vulcan carbon-supported and unsupported metallic Ir and rutile IrO 2 nanoparticles, and the process of Ir activation. For this purpose, we use large amplitude AC Voltammetry to distinguish between capacitive and faradaic processes. To quantify the data, we also use a mechanistic fit of the resolved harmonics. We show that all catalysts share the same OER mechanism but require different amounts of activation cycles. We have found three intrinsic properties, which can adequately describe a material for electrocatalysis. First is the activation threshold number (ATN), second is the current normalized to the number of active sites (intrinsic current), and lastly the mass normalized active site density. It was found that Ir on Vulcan has an intrinsic activity at least 3 times higher than the other two materials under consideration, as well as having the highest active site density. From the model fits we can also gain further insight into the mechanistic details for each material. For metallic Ir samples, the rate-limiting step is shown to be water adsorption, whereas for IrO 2 the bottleneck is the inherently slower kinetics. This also indicates that IrO 2 does not produce the same IrOH as Ir metal and therefore has different intrinsic properties. This study provides new insights into the intrinsic properties of different Ir nanocatalysts and highlights a general approach to studying the reaction mechanisms and intrinsic properties of electrocatalysts. [ABSTRACT FROM AUTHOR]

Photocatalysts can be used both for air cleaning and solar energy harvesting through water splitting. However, pure TiO 2 photocatalysts are often inefficient and therefore co-catalysts are needed to improve the yield. To achieve this goal, we prepared TiO 2 and deposited Pt, Ir and Ru co-catalysts on its surface. Two base TiO 2 nanoparticles were used: P25 and rutile TiO 2 synthesized via hydrothermal method. Co-catalysts were deposited by wet impregnation technique using single element and a combination of two elements (Pt and Ir or Pt and Ru), followed by annealing in either air or H 2 /Ar. Annealing in reducing atmosphere increased the photocatalytic activity of oxidation of isopropanol compared to annealing in air. We demonstrated a clear influence of the co-catalysts on the photocatalytic degradation of isopropanol and on electrochemical water-splitting reaction. The platinum-containing samples showed the best HER activity. • TiO 2 deposited with single co-catalysts (Pt, Ir, Ru) and their pairs (Pt/Ir, Pt/Ru). • Rutile with co-catalyst annealed in H 2 /Ar shows remarkably increased activity. • Rutile with Pt shows the highest activity in hydrogen evolution reaction (HER). • The deposited co-catalysts for all metals were in the 2–4 nm size range. [ABSTRACT FROM AUTHOR]

Abstract The field of electrosynthesis has undergone a tremendous advancement in the past few decades by implementation of a catalyst at the nanoscale level. While significant knowledge on factors that influence the activity of specific reactions such as carbon-halogen (CX) bond activation has been gained, many questions regarding the stability and degradation of nanoparticles still remain unsolved. Through the combination of a three-folded advanced characterization approach that combines electrochemical, analytical and microscopic results we are for the first time able to map the degradation of nanoparticles for CX bond activation reaction. This methodology is exemplified on the stability study of the most active nanoparticles towards CX bond activation, namely Ag nanoparticles. Results indicate that under electrochemical operation conditions Ag nanoparticles degradation occurs via two mechanisms: (i) agglomeration/coalescence and (ii) electrochemical dissolution of nanoparticles in the electrolyte. Identification of these degradation mechanisms is a first step in the understanding and subsequently controlling the synthesis of active and sustainable catalyst towards industrial applications. [ABSTRACT FROM AUTHOR]

Ø Electrodeposition of chloride-free Cu NCs. Ø Activation of Cu NCs by appropriate electrochemical protocol. Ø Support effect towards the selective formation of methane on Cu NCs. Ø Influence of electrochemical double layer cycling and OCP in tuning the activity and selectivity of Cu NCs. Nowadays, electrochemical CO 2 reduction reaction (CO 2 RR) to value-added products represents one of the major challenges in electrocatalysis. Copper-based nanocubes (Cu NCs) have been proposed as the front-runner's catalyst for the production of C 2+ products at the industrial level. However, their selectivity (C 1 vs. C 2 product distribution) is rather complex depending on the dynamic structural transformations, the presence of mixed Cu+/Cu0 states, the microenvironment, and nanocatalyst-support interactions. Commonly, electrochemically-grown Cu NCs are prepared in the presence of chlorides that acts as a shaping agent. In this study, an optimized electrodeposition method for the synthesis of Cl−-free Cu 2 O nanocubes on a glassy carbon substrate with uniform size, shape, and loading is established. The successful preparation of chloride-free cuprous oxide nanocubes (Cu 2 O NCs) was confirmed with X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses. We report how the electrochemical double-layer capacitance (EDLC) method for electrochemical surface area (ECSA) determination with(out) subsequent return to the open-circuit potential (OCP) conditions before electrolysis influences the CO 2 RR activity/selectivity. When Cu 2 O NCs are subjected to the EDLC method (often considered a non-invasive method) and exposed to the OCP before electrolysis, they become active for methane (CH 4) formation. Moreover, the influence of the potential window width (i.e. 200 and 400 mV) in which the EDLC-ECSA is employed and its correlations with the selectivity is presented. We underline the importance of the ECSA determination method and OCP on/off state as a triggering factor for reactivity/selectivity of particular Cu 2 O NCs for CO 2 RR and further emphasize the reconstructive nature of Cu 2 O NCs under CO 2 RR relevant conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• An efficient TiO x N y electro catalyst was synthesized in the immobilized form. • In-depth characterization of the active titanium oxynitride catalyst was performed. • A continuous-flow microreactor was used to study phenol degradation. • Oxidation mechanism was proposed including contribution of Cl− reaction pathways. • Optimal reactor dimensions were determined by the model. In this study a novel titanium oxynitride electrocatalyst was synthesized and its electrocatalytic activity for the degradation of phenol was evaluated. A highly conductive and efficient Ti–O–N electrocatalyst was prepared in a three-step synthesis. A titanium coil was anodized to grow TiO 2 nanotubes, which were then annealed in air to convert the amorphous structure to anatase and afterwards annealed in ammonia to obtain the final Ti–O–N catalyst. This was characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). To evaluate its degradation capabilities, the electrocatalytic oxidation of the phenol was performed inside a coil-type electrocatalytic microreactor. Phenol conversions of up to 95% of the initial 0.4 mmol L–1 of phenol were achieved at the studied applied electric potentials (1–16 V), NaCl concentrations (0.51–5.12 g L–1) and flow rates(20–500 μL min–1). The mechanism of electrocatalytic oxidation was proposed in a three-dimensional reactor model that accurately describes the electrocatalytic degradation of phenol at the Ti–O–N anode in the presence of NaCl in the phenol solution. It was shown that both OH*– and OCl*–mediated reaction mechanisms contribute to the phenol's degradation, while at high NaCl concentrations (5 g L–1) the latter is dominant. In addition, the optimal reactor design is determined by studying the mass-transfer limitation with the model. [ABSTRACT FROM AUTHOR]